Buckmasters Magazine

Hunting Below the Threshold

By Jeff Murray

You can’t stop 100% of human scent, but you can reduce it to a huntable level.

Is it humanly possible to not smell like a human? I often kick off seminars with this question because it’s a hot, if not the hottest, topic in hunting. Invariably, the “nays” outnumber the “ayes” by at least three to one.

Someone might answer, “Depends on what ‘smell like a human’ means.” Bullseye! If you want to beat a buck’s nose, take note: Applying the science of scent control, it is possible to turn a whitetail’s strongest defense into its Achilles’ heel. What follows is a journey into the fascinating world of olfaction, detection and dilution — scent control’s Big Three. Capitalizing on them delivers the net effect of hunting “below the threshold.”

OLFACTION: The Sense of Scent Perception

A whitetail’s primary interaction with its environment is through olfaction, or sense of smell. It is its keenest defense, and it functions like radar. Deer can detect odors that are undetectable to humans because their noses are endowed with countless specialized receptor cells in an extra-large nasal cavity. This enables them to pinpoint and age most scent sources with extraordinary accuracy. Slight differences in the number and location of triggered receptors tell deer how to respond to various odorous stimuli.

Now here’s where things get chancy.

It’s crucial that hunters neither overestimate nor underestimate this olfactory system. To get an accurate view of what we’re up against, let’s first quantify a deer’s sense of smell. Most researchers I’ve interviewed agree that ungulates can smell whatever canines can smell. But this can be misleading. For instance, scientists with the British Columbia Research Council have determined that a dog can perceive some odors (such as acetic and butyric acid) at concentrations a million times lower than humans, but other odors (such as mercaptan and ionone) only about a thousand times better.

Apparently, if dogs (and deer) are equipped to smell something we humans can’t, their sensitivity is far greater; conversely, if we’re both equipped to detect a particular odor, the gap is considerably narrower.

This brings us to an alarming fact: A deer’s sense of smell is a closed loop; it operates independent of the conscious level. Your knee’s reflex reaction, when struck with a doctor’s rubber hammer, is a good analogy. It responds without any thinking whatsoever. In fact, the harder you try to beat it, the worse it seems to get. If you forget anything about a deer’s nose, don’t forget this: About two-thirds of its brain is dedicated to the detection, perception and evaluation of odors with no higher thinking or problem-solving involved. This is why you can literally read a buck’s body language to know what his nose is telling him. But it’s also why you can use your brain to outwit his.

Salmon studies represent an interesting correlation. Researchers on the West Coast isolated an odor so repulsive that it literally halted upstream movement of spawning fish. Put another way, this particular odor triggered the fish’s survival instinct that, in turn, overpowered mating instincts.

For the record, the alarm odor was amino acid L-serine, which is found in high concentrations on the fingers and palms of humans. Interestingly, the only other agent found to halt salmon migrations is scent extracted from the footpads of bears.

Just as fishermen have learned to control L-serine, deer hunters can follow suit by systematically addressing the alarm odors our bodies produce.

DETECTION: The Source and Dispersion of Scent

Here’s a condensed explanation of how you might telegraph your presence in the deer woods: The first odorous clues we leave behind come from our footprints. Each foot possesses about 250,000 sweat glands and, in one day, can produce up to a pint of sweat per foot. Before long, bacteria dining on this sweat begin excreting their inimitable pungent waste. It gets worse.

Since foot sweat can’t evaporate efficiently like sweat on the hands or back, it piles up in socks, boot liners and insoles where a microscopic feeding frenzy takes place. According to Dr. Don Thompson with North Carolina State University, these odor compounds number in the thousands, not dozens, making scent-control a tricky task.

Take the ever-popular rubber boot. It could make matters worse. Rubber is gas-permeable (all odors are gases) so foot odor eventually leeches through these boots. Further, rubber boots provide an ideal environment — warm, moist, dark — for colonizing fungi. Even worse, the calf-high design worn by many bowhunters is an efficient scent-dispenser; instead of depositing trace odors near the ground, it pumps them airborne, where air currents spread them greater distances. Finally, rubber boots hold a noticeable factory odor that’s difficult to remove.

Back to our trek to the treestand. Whatever we touch along the way — grass, brush, tree branches, leaves — becomes contaminated with butyric acid from our palms and fingers. Interestingly, this is the base ingredient responsible for the odor of vomit. And, believe it or not, it’s detectable to the human nose at extremely low levels — only .00028 ppm (parts per million).

By now our back, underarms, knees and groin are sweating. Like ravens on a roadside telephone wire, bacteria are lining up to devour the sweat excreted from apocrine glands located at these body parts. Complicating matters is the simple fact that bacteria require an incubation period to produce body odor. This means garments will smell worse and worse until bacteria are removed with a thorough cleansing.

I’ve saved the worst for last. In spite of the many odor sources identified so far, their accumulative effect pales in comparison to that of human breath. The consensus is that mouth-related odors contribute between 85 and 90 percent to what whitetails detect as human odor. Consider the following:

• Breathing involves 2,000 inhales and exhales per hour. This gives winds and thermals a constant source of odor molecules to disperse in the immediate area.

• The mouth’s waste products, resulting in bacterial action, are mostly sulfur compounds. They are extremely foul-smelling at very low concentrations and are the main cause of halitosis.

• Some of these volatile sulfur compounds (VSCs) are familiar odors that we find extremely offensive: methyl mercaptan (causes the smell of hogs and turkey feed lots), dimethyl sulfide (decaying seaweed from an ocean backwater, and hydrogen sulfide (rotten eggs).

So as we climb our treestands, we’re sweating and breathing heavily. And we’re still not done telegraphing our presence. As we scale the tree, we leave more clues behind every inch of the way — on tree steps, the trunk of the tree, and limbs. Now it’s time for gravity to assist the dispersal of scent. Odor molecules from our mouth begin to pile up at the base of the stand like a fresh blanket of snow. And since these odor molecules tend to be large and heavy, the surrounding area becomes more contaminated than we can imagine.

Lastly, dead skin cells add to the mix; our epidermis sloughs off tiny granular particles that continually rise to the surface from the dermis.

By the end of the day, we haven’t seen a single deer, and we wonder why.

DILUTION: The Science of Scent Threshold

Since man first sharpened a stick, big-game hunters have employed a virtual encyclopedia of strategies to avoid scent detection. North American Indian tribes tried masking their scent with a stronger odor, typically smoke or tannic acid from a pond. In the 1970s, hunters expanded the masking technique with everything from vanilla to the essence of skunk. If masking worked, this story would end right here. But even a human nose can detect two or more odors simultaneously.

The reason a masking scent doesn’t work is Scent Detection 101. Simply stated, for an odor to be perceived, it must reach a specific threshold, or concentration level. It is typically measured in parts per million. Any odor source falling short of this benchmark is feint and confusing, at best. This is what happens when you get a whiff of something but are unable to identify it.

Examples range from a distant fire to chocolate cookies baked an hour ago. This phenomenon forms the basis for all science-based scent-control strategies. If hunters learn to reduce their scent stream to below-threshold levels, they can, indeed, beat the nose that knows!

Hunting Below the Threshold

I often hear hunters complain about getting busted in spite of their investments in odor-control technologies. While some products are not a match for diluting the full spectrum of the human scent stream, I wonder if operator error is the real culprit. Until a couple of years ago, I found myself making dumb moves that cost me close encounters. In sum, if you play the game by all of the rules, deer will either think you’re farther away than you really are, or that you passed by much earlier.

To illustrate this principle, let’s rehearse the system, step-by-step, for hunting below the threshold.

• Start fresh. The cleaner you are, the fewer odors your body produces, and the more efficient and longer-lasting your Scent-Lok or ScentBlocker or Moxy or Ozonics system will be. Naturally, unscented soaps and shampoos get the nod over commercial potions. But did you know that shaving underarm hair can increase a deodorant’s effectiveness several-fold? Bet you also didn’t know that rotating formulas prolongs anti-bacterial action. What works best for me, for example, is a rotation of Unscented Ultra Max (Arm & Hammer formula) and a mixture of Robinson Outdoors’ Body Shield Gel and baking soda.

• Clean clothes right. Before initial use, wash all hunting clothes with an unscented sport concentrate designed specifically to avoid clogging pores of high-tech fabrics. But first, run a rinse cycle through the washer to remove household detergent residue.

• Store right. For optimum storage and transport, always use a scent-free container like ScenTote’s unique system (www.scentote.com) or Scent-Lok bags (www.scentlok.com).

• Reactivate right. Before you reactivate carbon clothing with the high-heat setting of a clothes dryer, first wipe the drum with a towel doused in a quality odor-control spray.

• Cover your mouth. Never breathe in your hunting area without wearing a scent-controlling mask or hood.

• Keep your cool. The less you sweat, the less food bacteria have to dine on, and the fewer wastes they excrete. Under-dress while walking and add layers, including socks, from your pack when you get to your hunting destination.

• Fancy footwork. Subscribe to a science-based footwear regimen, starting with waterproof, breathable boots. Consider including an activated insole, such as Robinson’s Dynamic Support Carbon model, and covering the tops of boots with treated or carbon-lined pants. Take advantage of odor-eliminating clothing’s drawstrings and buttoned flaps to seal off and trap foot odors. Also rotate pairs of boots, airing, drying out and treating boots between hunts.